I have encountered the same problem a few times and i have
realised that it happens if the audio clip size is too small (less
than or equal to 8KB). Audio clip of this size may get associated
with a slide in any one of these workflows :
1. If user records a single syllable word such that size of
the mp3 is less than 8KB.
2. If user imports an audio file of size less than 8KB (the
duration of such a file will be less than 1 sec at 128kbps bit
3. If user edits audio in a presentation in Audio Editor,
leaves a clipping of duration less than 1 sec on a slide and later
copies this slide to some other presentation.
Have you done any of the above things in your presentation?
Another way of checking is to go to the asset folder and see the
duration of all the audio clips in the 'audio' folder. Do you see
any clip with duration 00:00 or 00:01 secs?